Thanks Chester! I've had those experiences too!
This one is so simple and is from the factory, I
thought I'd try it. Easy to put back if it causes any
problem.
Anthony
--- Chester <calderman@cox.net> wrote:
> I would like to add some personal experience to
> this.
>
> I bought my Omni 6 in 1992 and the darned thing just
> worked beautiful in
> terms of front end overload. I had no test equipment
> to check IMD, but I
> thought I would IMPROVE the IMD (which did not need
> improvement in the
> first place!).
>
> Being an amateur, I was SURE I could improve on what
> Ten Tec's engineers
> had done, in terms of their selection of 'cheap'
> pin-diodes. So I
> removed the BPF/Front End board, very carefully
> removed diodes D7
> through D30, and replaced each of Ten Tec's 'cheap'
> pin-diodes with the
> more expensive and 'better' (and Mr. Rhode's
> recommended) HP-5082-3081
> pin-diodes. Since the best operating point of the HP
> diodes occurred
> with about 100ma flowing through them, I had to
> decrease the value of
> R14, R15, R25, and R26. Took several hours and very
> careful soldering,
> but I knew it would be better!
>
> WRONG!! Disaster! Seriously degraded the IMD
> performance and I began to
> hear severe front end overload in the presence of
> strong signals,
> especially on 80m and 40m during heavy CW DX
> contest! Being the smart
> amateur I am, I threw away Ten Tec's 'cheap'
> pin-diodes and thus could
> not repair the BPF/Front End board. A replacement
> board cost $765. I
> didn't replace it, just to provide me with a
> constant reminder to keep
> my cotton-picking fingers out of something that was
> not broken to begin
> with!
>
> YMMV!
>
> Tom/W4BQF
>
> Chester Alderman
> calderman@cox.net
>
> -----Original Message-----
> From: tentec-admin@contesting.com
> [mailto:tentec-admin@contesting.com]
> On Behalf Of Anthony Bowyer
> Sent: Wednesday, January 15, 2003 8:30 AM
> To: tentec@contesting.com
> Subject: [TenTec] Omni VI Resistor circuit locations
>
>
> An early post by KL7HF concerning the Omni VI 2nd
> order IMD mod:
>
> Locate the PBF/Front End Board, and remove. (Bottom
> under the shield.) Identify R-14, a 470 ohm resistor
> immediately adjacent to connector 24. Remove and
> replace with a 220 ohm resistor.
> Now - with the board positioned to where the
> resistor
> you just changed is next to you, and with the
> connectors 18 and 17 to you left, look for another
> 470
> ohm resistor directly to the left of connector 24.
> There will be three others between it and connector
> 24.
> Remove that resistor and replace with a jumper.
> That is all there is. The second resistor is not
> marked, so is a bit hard to tell you where it is,
> with
> out a picture!
> Good Luck. de KL7HF
>
>
> Could someone on the list with an Omni VI manual do
> me
> a big favor? I'm trying to find out where R-14 (470
> ohm) and the other 470 ohm resistor mentioned above
> is
> in the circuit on the band pass board. I thought it
> might be benificial to make this change on an Omni
> V,
> but the part designations and board layout is a bit
> different. Of course, it might be different enough
> on
> the V so it can't be done anyway, but thought I'd
> take
> a look. I assume this mod changes the bias on the
> switching diodes for the band pass filters.
>
> Any help is greatly appreciated!!!
> Anthony
>
>
>
> =====
> NT4X
>
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=====
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